Ancestors' exposure to DDT may contribute to obesity, study says

A crew sprays a solution containing DDT in an alley in Santa Monica in 1948.

A crew sprays a solution containing DDT in an alley in Santa Monica in 1948. (Los Angeles Times Archive)

Tony Barboza

Exposure to the pesticide DDT could be playing a role in high rates of obesity three generations later, a new study says.

Scientists injected pregnant rats with DDT and found no change in their levels of obesity or their offspring. But by the third generation, more than half of the rats (think of them as the great-grandchildren) showed dramatically higher levels of fat and weight gain, even though they were never exposed to the pesticide themselves.

"Here is an ancestral exposure in your great-grandmother, which is passed on to you and you’re going to pass on to your grandchildren," said Michael Skinner, a professor of biological sciences at Washington State University who led the research published in the journal BMC Medicine.

A series of experiments on lab rats found that chemicals known as endocrine disruptors, including fungicides, dioxin and bisphenol-A, or BPA, can alter the molecular processes around their DNA without changing its sequence, Skinner said.

The contaminants can turn genes on or off and be passed on to descendants generations down the line, leading them to develop conditions like kidney disease, ovarian disease or obesity.

"We’ve all been taught that the primary way for us to inherit things from our parents is genetics," Skinner said. "This is a totally new concept for how we inherit things from our ancestors."

Though the study makes no conclusions about the risk to humans, Skinner said it should give pause to those advocating the use of DDT to combat malaria more than 50 years after Rachel Carson’s book "Silent Spring" brought attention to the pesticide’s lasting damage to the environment.

DDT was banned in the United States in 1972, but more recently, the World Health Organization and other global health groups have backed using the insecticide to control mosquitoes in countries with high rates of malaria.

"Although the number of lives saved from malaria is significant, the long-term health and economic effects on survivors and subsequent generations also need to be considered," the study says.